1. Technical Field
The present invention relates to a frequency analyzer for a MEMS based cochlear implant with self power supply, and more particularly, to a frequency analyzer for a MEMS based cochlear implant that enables the cochlear implant without any battery for power supply to be implanted in the human body and has a self power supply function without using conventional complex units such as a microphone, a speech processor, and a wireless electricity supply.
2. Description of the Related Art
As illustrated in FIG. 1, there exist a basilar membrane decomposing sound according to its frequencies and stereocilia disposed at the upper end of the basilar membrane to convert sound information to electrical signals and transmit the electrical signals to the brain through nerves in a cochlea of a mammal.
The typical human cochlea operates over a 3-decade frequency band, from 20 Hz to 20 kHz, covers 120 dB of dynamic range, and can distinguish tones that differ by less than 0.5%. The cochlea is also very small and occupies a volume of approximately 1 cm3. Perhaps most importantly, the cochlea uses a mechanical process to separate audio signals into approximately 3,500 channels of frequency information. Thus, the cochlea is a sensitive real-time mechanical frequency analyzer.
As illustrated in FIG. 2, the currently used cochlear implant includes a microphone, a speech processor, a transmitter/receiver, and an array of electrodes. The cochlear implant has up to 22 channels. The microphone converts sound wave signals to electrical analog signals, and the speech processor performs signal processing such as conversion of time based electrical analog signals to frequency based electrical digital signals on the basis of the digital signal processor (DSP) technology. The transmitter/receiver wirelessly transmits signals of the speech processor outside the body into the body.
As illustrated in FIG. 3, a basilar membrane in a cochlea has a thick and narrow structure in a base region to be resonated by high-frequency waves and has a thinner and wider flexible structure as it goes toward an apex region.
Thus, as illustrated in FIG. 4, electrodes are inserted into a cochlea to stimulate auditory nerves distributed from the base (high-frequency region) to the apex (low-frequency region), generating bioelectrical signals and transmitting the information to the cochlear nucleus in a brain stem.
However, the conventional cochlear implant system includes a complex structure having a microphone, a speech processor, and a transmitter that are attached outside a human body, and a receiver, a stimulator, and electrodes that are implanted in the human body, so a large and expensive electronic circuit chipset is necessary and a large amount of power is consumed, increasing the price of the entire system. Moreover, a large capacity battery and an auxiliary unit are necessary to generate electrical signals, and in most cases, the lifespan of the battery is limited to from several hours to below one week, requiring frequent recharges of the battery.
Further, since the use of the DSP in the conventional cochlear implant system causes delay of audio signals up to several tens of seconds and the electrical signals are encoded to be wirelessly transmitted to an electronic circuit in the skull, only a limited number of channels can be processed.
Furthermore, a cochlear implant system is practical and its listening quality is most important regardless of its appearance. However, although the cochlear implant systems suggested until now allow the users to distinguish simple spoken words, the users have difficulty in appreciating music and distinguishing tones of languages.